Pipelines can develop flaws over time. If left uncorrected, such flaws may eventually result in catastrophic failure of the pipeline. Such a catastrophic failure may result in lost services and revenues, and possible environmental damage. Because a pipeline may fail without warning, early detection of flaws is fundamental to preventing catastrophic failure.
A wide variety of pipe inspection systems that carry or draw inspection equipment through a pipeline are known. These inspection systems, generally referred to as pipe crawlers, pipe inspection pigs, and the like, are used for inspecting the interior walls of piping systems for damaged or flawed structural features. These pipe inspection systems can be propelled through a pipeline by pipeline flow, by manually drawing the inspection system through the pipe with cables and winches, and/or by self-propelling mechanisms.
The mechanics of passing an inspection system through a pipeline present several problems. For example, a problem that exists in some inspection systems is that they contain components that are unable to negotiate sharp bends or junctions. These systems are therefore unsuitable for use with convoluted pipelines. In addition, an inspection system that is unable to negotiate the bends and junctions in a pipeline is likely to become jammed in the pipeline. If an inspection system becomes stuck within a pipeline, then the system itself becomes a “flaw” (i.e., a blockage) of the pipeline, necessitating repair.
Inspection systems that are propelled by pipeline flow are not always appropriate in particular situations. For example, pressure or flow propulsion may not be adequate for severely leaking pipes, and cannot be used in empty pipes.
For inspection systems that are pulled through a pipeline by a towline, the towline may produce a significant amount of friction. For example, it takes considerable force to simply drag a half-inch steel cable through a two-kilometer steel pipeline. In addition, the cable poses a significant hazard to the pipeline, especially at bends and junctions where the dragging of the cable may actually cut into the inner surface of the pipeline.
An umbilical line is often used to power the electronic components of a self-propelled system and to bring out the resultant data. Since the umbilical line is not being used as a towline, much less force is imposed on the umbilical line, resulting in less potential damage to the pipeline.
Nevertheless, whether it utilizes a manually drawn towline or an umbilical line for power, the range of action of the inspection system is limited because of the friction resistance of the cable to be dragged along on the walls of the pipe. This friction resistance increases with increasing distance from the starting point, after negotiating several pipe elbows, and/or if the inspection system must negotiate steep inclines or vertical pipe sections.
Sufficient traction, i.e., the friction between the inspection system and the pipe wall, may overcome some of the problems associated with friction resistance of the dragging cable, and may facilitate negotiation of inclines and/or vertical pipe sections. Self-propelled inspection systems have typically been propelled with wheels that are rollingly held against the pipe wall. Unfortunately, the traction of the wheels in any sludge, which may have accumulated at the bottom of the pipe, is sometimes insufficient, thus causing the wheels to slip. The traction of the wheels has also typically been insufficient in prior art devices when the inspection system is propelled up an incline and/or up a vertical pipe section.
One prior art pipe crawler attempts to mitigate the problem of insufficient traction through the implementation of continuous treads spaced apart peripherally in lieu of wheels. Drive motors transmit motive force through transmission gearing to drive wheels for the continuous treads. The vehicle travels through the pipe along an inner wall surface as the continuous treads are driven by the drive wheels. Diametrically opposing pairs of continuous treads are mounted in opposing relationship for outward movement in opposite directions, and tread biasing means is disposed between the pair of continuous treads so as to effect the outward movement. Tread biasing means generally includes a spring system external to each of the continuous treads so as to interconnect a pair of continuous treads.
While such continuous treads may impart larger traction forces toward the pipe walls then wheeled units, this prior art pipe crawler has several problems. For example, retraction or extension of the spring system causes the linked pair of continuous treads to move inwardly or outwardly relative to one another. As such, the size of the passage between the pair of continuous treads is subject to change, potentially causing damage to cabling passing through the central passage. In addition, since the same spring force is imposed on both continuous treads of the linked treads, the system is not self-centering within a pipe which could be problematic for attached inspection devices and when negotiating bends or curves in the pipe. Furthermore, the diametrically opposed pairs of continuous treads cannot move independent from one another in order to accommodate variations in the pipe wall.
Additionally, orthogonally oriented pairs of continuous treads, i.e., those oriented at right angles from one another, of this prior art pipe crawler, are linked via the motor transmission gears. Accordingly, when the springs between the diametrically opposed pairs of continuous treads extend or retract in response to pipe diameter, the gears of the orthogonally oriented pairs of continuous treads may become misaligned and bind, potentially causing the vehicle to malfunction. In addition, this transmission gearing system prevents independent speed control of the continuous treads, thereby yielding restricted maneuverability.
Accordingly, what is needed is a self-propelled vehicle with traction sufficient to negotiate inclines, vertical pipe sections, and sludge laden pipe sections. What is further needed is a self-propelled vehicle that is self-centering, readily maneuvered, compact, and robust in design.